A run of four league defeats from late November issued a reality check at the south coast club but dreams of a top-four finish once again seem realistic with 10 points taken from the last 12 on offer.

Saints in rare territory

Southampton started a calendar year in the top four in the Premier League for the first time since 1990.

Without the suspended Morgan Schneiderlin - a reported target for many teams in January - Koeman's side were solid all over the pitch, none more so than goalkeeper Forster, who saved brilliantly from Santi Cazorla and Sanchez either side of Mane's opener.

By contrast, Szczesny made errors which proved the difference between the teams.

First, the Poland keeper raced from his goal to confront Mane, but the Senegal striker - soon heading for the African Cup of Nations - curled in his third goal in as many games with a measured finish from the byline.

The Arsenal keeper then superbly denied James Ward-Prowse from 12 yards before the break, but panicked when grounded in his six-yard box before the hour mark and kicked a loose ball straight to Tadic, who scored his second Premier League goal.

The Arsenal keeper instantly sipped his sports bottle with a bemused look on his face. It was the seventh goal his side have conceded from an error this season - only Everton, with 11, have more.

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Wenger rues 'two big mistakes'

The Gunners nearly added to that tally when Szczesny was sold short by a backpass and Mathieu Debuchy was left to clear Pelle's prod off the line.

Pelle had more shots than any other Premier League player in the first half of the season and also came close to adding to his eight league goals when he struck the post in each half.

His missed chances underlined the volume created by the home side but they were fortunate to end with 10 men when Florin Gardos - the last man - felled Alexis Sanchez with a quarter of the game remaining.

Referee Craig Pawson issued only a yellow and despite Arsenal introducing Theo Walcott for the first time since November, they rarely threatened to reduce the arrears.

Former Arsenal defender Martin Keown on BBC Match of the Day:

"There are problems in that defensive area for Arsenal. They were second best. You have to look at what is in front of the goalkeeper. It is embarrassing and it is something we are seeing time and time again."

Graziano Pelle had five attempts at goal, hitting the post twice and seeing one cleared off the line

Per Mertesacker lunged but could not keep out Sadio Mane's curled effort as Szczesny raced back

Szczesny's second error landed at the feet of Dusan Tadic who scored his second league goal of the season

Arsene Wenger cut a frustrated figure on the touchline as his side struggled to hurt their hosts